From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id E3D78CFD313 for ; Mon, 24 Nov 2025 14:36:44 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 359296B002E; Mon, 24 Nov 2025 09:36:44 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 331366B002F; Mon, 24 Nov 2025 09:36:44 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 26D256B0030; Mon, 24 Nov 2025 09:36:44 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0014.hostedemail.com [216.40.44.14]) by kanga.kvack.org (Postfix) with ESMTP id 161306B002E for ; Mon, 24 Nov 2025 09:36:44 -0500 (EST) Received: from smtpin24.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay05.hostedemail.com (Postfix) with ESMTP id C4A4458E38 for ; Mon, 24 Nov 2025 14:36:43 +0000 (UTC) X-FDA: 84145751886.24.5EDA964 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by imf09.hostedemail.com (Postfix) with ESMTP id 63AFE14000B for ; Mon, 24 Nov 2025 14:36:41 +0000 (UTC) Authentication-Results: imf09.hostedemail.com; dkim=none; dmarc=pass (policy=none) header.from=arm.com; spf=pass (imf09.hostedemail.com: domain of ryan.roberts@arm.com designates 217.140.110.172 as permitted sender) smtp.mailfrom=ryan.roberts@arm.com ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1763995002; a=rsa-sha256; cv=none; b=DwecN+Fl8ES/hBPwm9GPtQ/xty76sC9VdXFTgvwQCaD5ENEmCTD3dwoslmfy/s2mtLKNZH 3IBgDdKua1DyVtcz9GlmRc5VGyfgroT/VVNtmmJCrjwFfRTe3xppvJmtH8G60f2ji/Pt3e hXIBe5/yKkDM6iowhtEOx9w3J2G7NCM= ARC-Authentication-Results: i=1; imf09.hostedemail.com; dkim=none; dmarc=pass (policy=none) header.from=arm.com; spf=pass (imf09.hostedemail.com: domain of ryan.roberts@arm.com designates 217.140.110.172 as permitted sender) smtp.mailfrom=ryan.roberts@arm.com ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1763995002; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=YJ471huPf3AbbCsoCzRDaoFvk+dd/VjhisJknTSiicY=; b=p1PUkBcyEJ23CAEbr+bTUavJGR+20MEMx1CPwOvY55nNIr4Q9S19bIBF0s57qn0wZf9x/h 3Domf3ww/tJJRuSTj0fD1DOwW6cI66Ehwnq8quEcQXCXvc+ROIaoneiKrtZE0SAg+q+kVT NOpdQ55srwEMRPtS4ZVV/zYS81K8/pc= Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 80775497; Mon, 24 Nov 2025 06:36:32 -0800 (PST) Received: from [10.57.88.238] (unknown [10.57.88.238]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 94CBA3F6A8; Mon, 24 Nov 2025 06:36:34 -0800 (PST) Message-ID: Date: Mon, 24 Nov 2025 14:36:32 +0000 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v4 06/12] mm: introduce generic lazy_mmu helpers Content-Language: en-GB To: Kevin Brodsky , linux-mm@kvack.org Cc: linux-kernel@vger.kernel.org, Alexander Gordeev , Andreas Larsson , Andrew Morton , Boris Ostrovsky , Borislav Petkov , Catalin Marinas , Christophe Leroy , Dave Hansen , David Hildenbrand , "David S. Miller" , David Woodhouse , "H. Peter Anvin" , Ingo Molnar , Jann Horn , Juergen Gross , "Liam R. Howlett" , Lorenzo Stoakes , Madhavan Srinivasan , Michael Ellerman , Michal Hocko , Mike Rapoport , Nicholas Piggin , Peter Zijlstra , Suren Baghdasaryan , Thomas Gleixner , Vlastimil Babka , Will Deacon , Yeoreum Yun , linux-arm-kernel@lists.infradead.org, linuxppc-dev@lists.ozlabs.org, sparclinux@vger.kernel.org, xen-devel@lists.xenproject.org, x86@kernel.org References: <20251029100909.3381140-1-kevin.brodsky@arm.com> <20251029100909.3381140-7-kevin.brodsky@arm.com> <71418b31-aedb-4600-9558-842515dd6c44@arm.com> From: Ryan Roberts In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-Rspamd-Queue-Id: 63AFE14000B X-Rspamd-Server: rspam07 X-Stat-Signature: xf7cunn4t8jap43pjqzhhf8sapuypauz X-Rspam-User: X-HE-Tag: 1763995001-360749 X-HE-Meta: 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 B8HAQELA ui3gIzuwtxBWchqiMTxchAENwj5cyXWoWeqlD53QVLB4+vONg1i5a/eyscZG9ZJMGwyxOaWnzwBbi9BsjeCB/oErpZwf5rutg/7QOzaexU5q83HYHdIZx7eyAhqaDXcg0bpoUnSarogMezQZfo/Pfmx0J4bf5ABq8A4ngrNp71W8GAixFEHBU59AENVPXFRTpd0v0KL0SXNIGkINfPoc2XQj3ZQ== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 24/11/2025 12:47, Kevin Brodsky wrote: > On 10/11/2025 11:45, Kevin Brodsky wrote: >>>> diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c >>>> index b8d37eb037fc..d9c8e94f140f 100644 >>>> --- a/arch/arm64/mm/mmu.c >>>> +++ b/arch/arm64/mm/mmu.c >>>> @@ -731,7 +731,7 @@ int split_kernel_leaf_mapping(unsigned long start, unsigned long end) >>>> return -EINVAL; >>>> >>>> mutex_lock(&pgtable_split_lock); >>>> - arch_enter_lazy_mmu_mode(); >>>> + lazy_mmu_mode_enable(); >>>> >>>> /* >>>> * The split_kernel_leaf_mapping_locked() may sleep, it is not a >>> This is a bit unfortunate, IMHO. The rest of this comment explains that although >>> you're not supposed to sleep inside lazy mmu mode, it's fine for arm64's >>> implementation. But we are no longer calling arm64's implementation; we are >>> calling a generic function, which does who knows what. >>> >>> I think it all still works, but we are no longer containing our assumptions in >>> arm64 code. We are relying on implementation details of generic code. >> I see your point. The change itself is still correct (and required >> considering patch 8), but maybe the documentation of the generic >> interface should be clarified to guarantee that the generic layer can >> itself cope with sleeping - without any guarantee regarding the >> behaviour of arch_*_lazy_mmu_mode. > > Re-reading the existing comment in , I think it already > makes clear that sleeping is not forbidden by design: > >>  * In the general case, no lock is guaranteed to be held between entry >> and exit >>  * of the lazy mode. So the implementation must assume preemption may >> be enabled >>  * and cpu migration is possible; it must take steps to be robust >> against this. > > The arch implementation may disable preemption, but arm64 code can rely > on the arm64 implementation allowing sleeping. Yeah ok, I buy that! > > - Kevin >